Before the USB core resets a device, we need to disable the L1 timeout for the roothub, if USB 2.0 Link PM is enabled. Otherwise the port may transition into L1 in between descriptor fetches, before we know if the USB device descriptors changed. LPM will be re-enabled after the full device descriptors are fetched, and we can confirm the device still supports USB 2.0 LPM after the reset. We don't need to wait for the USB device to exit L1 before resetting the device, since the xHCI roothub port diagrams show a transition to the Reset state from any of the Ux states (see Figure 34 in the 2012-08-14 xHCI specification update). This patch should be backported to kernels as old as 3.2, that contain the commit 65580b4321eb36f16ae8b5987bfa1bb948fc5112 "xHCI: set USB2 hardware LPM". That was the first commit to enable USB 2.0 hardware-driven Link Power Management. Signed-off-by: Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx --- drivers/usb/core/hub.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c index 3f8933f..d3a1d79 100644 --- a/drivers/usb/core/hub.c +++ b/drivers/usb/core/hub.c @@ -5090,6 +5090,12 @@ static int usb_reset_and_verify_device(struct usb_device *udev) } parent_hub = usb_hub_to_struct_hub(parent_hdev); + /* Disable USB2 hardware LPM. + * It will be re-enabled by the enumeration process. + */ + if (udev->usb2_hw_lpm_enabled == 1) + usb_set_usb2_hardware_lpm(udev, 0); + bos = udev->bos; udev->bos = NULL; -- 1.8.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
